Method of fabricating precision pagewidth assemblies of ink jet subunits

ABSTRACT

A method of fabricating extended arrays of image reading or writing subunits and in particular a pagewidth thermal ink jet printhead from a plurality of discrete thermal ink jet printhead subunits is disclosed. Each thermal ink jet printhead subunit includes a heater plate subunit having a plurality of resistive elements on an upper surface thereof and a channel plate subunit having a plurality of channels corresponding in number and position to the resistive elements on a base surface thereof, the upper surface of the heater plate subunit being attached to the base surface of the channel plate subunit to define a thermal ink jet printhead subunit having a plurality of channels forming nozzles with a resistive element in communication with each channel. The method includes the steps of forming a precision alignment structure such as a notch with, for example, a precision dicing saw, on an upper surface of each channel plate subunit, placing the upper surface of each discrete thermal ink jet printhead subunit on an elongated alignment substrate having a plurality of corresponding alignment structures, and engaging the upper surface of each discrete thermal ink jet printhead subunit with one of the corresponding alignment structures on the alignment substrate. These steps are repeated with subsequent thermal ink jet printhead subunits until an extended array having the length of, for example, a pagewidth is formed. The array of thermal ink jet printhead subunits are then bonded to, for example, a base substrate to form an integral pagewidth printhead.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to methods of fabricating extended arraysof silicon wafer subunits, and more particularly to methods of formingpagewidth thermal ink jet printhead arrays from discrete thermal ink jetprinthead subunits.

2. Description of Related Art

With the increased interest in rastor scanners, both to read and writeimages, has come renewed demand in the art for an economical full widthscanning array. In the current stage of scanner technology, the art iswithout a commercially acceptable and economically feasible method ofproducing very long unitary scanning arrays, that is, single arrays ofsufficient linear extent and with the requisite number of imageprocessing elements to scan an entire line at once with a high imageresolution. In this context, when speaking of scanning arrays, there areboth image reading arrays which comprise a succession of image sensingelements such as, for example, photosites and supporting circuitry, toconvert the image line to electrical signals or pixels, and imagewriting arrays which comprise a succession of light producing or otherelements employed to produce images in response to an image signal orpixel input.

The prior art has faced this failure or inability to provide long fullwidth scanning arrays with various proposals. These include optical andelectrical arrangements for overlapping plural shorter arrays andabutting short arrays together in end-to-end arrangements. However, noneof these proposals has met with any great degree of success. Forexample, in the case of abutting smaller arrays together, due to thedifficulty of exactly aligning and mating the array ends with oneanother, losses and distortion of the images often occur.

A similar problem arises with thermal ink jet printing systems. Thermalink jet printing systems use thermal energy selectively produced byresistors located in capillary filled ink channels near channelterminating nozzles or orifices to vaporize momentarily the ink and formtemporary bubbles on demand. Each temporary bubble expels an ink dropletand propels it towards a recording medium. The printing system may beincorporated in either a carriage type printer or a pagewidth typeprinter. The carriage type printer generally has a relatively smallprinthead, containing the ink channels and nozzles. The printhead isusually sealingly attached to a disposable ink supply cartridge and thecombined printhead and cartridge assembly is reciprocated to print oneswath of information at a time on a stationarily held recording medium,such as paper. After the swath is printed, the paper is stepped adistance equal to the height of the printed swath, so that the nextprinted swath will be contiguous therewith. The procedure is repeateduntil the entire page is printed. For an example of a cartridge typeprinter, refer to U.S. Pat. No. 4,571,599 to Rezanka. In contrast, thepagewidth printer has a stationary printhead having a length equal to orgreater than the width of the paper. The paper is continually moved pastthe pagewidth printhead in a direction normal to the printhead lengthand at a constant speed during the printing process. Refer to U.S. Pat.No. 4,463,359 to Ayata et al for an example of pagewidth printing andespecially FIGS. 17 and 20 therein.

Thermal ink jet printers include printheads, such as side shooterprintheads shown in FIG. 1 and described in U.S. Pat. No. 4,601,777 toHawkins et al (the disclosure of which is herein incorporated byreference). It is desirable to form these printheads having the width ofa page to enable high speed printing to be performed. One method offorming these pagewidth printheads, illustrated in FIG. 1, involvesbutting together a plurality of printhead subunits S₁, S₂, S₃ to form aprinthead array having the length of a pagewidth. With the sideshooterprinthead, each printhead subunit includes a heater plate 2 having aseries of resistive heater elements 3 located on an upper surfacethereof attached to a channel plate 4 having a series of channels 6located on a lower surface thereof and corresponding in number to theresistive heater elements. The end of each channel 6 forms a nozzle fromwhich a drop of ink is outputted upon actuation of the correspondingresistive element 3. One method of forming such pagewidth printheadsfrom an array of printhead subunits involves flipping each printheadsubunit S₁, S₂, S₃ upside down and physically butting it to an adjacentprinthead subunit. The channel plate 4 is etch delineated to be lesswide than the heater plate 2, which can be precisely delineated by aprecision dicing saw. With such a configuration, the channel plate playsno part in the physical butting process and only the precisely dicedheater plate 2 determines the subunit-to-subunit placement accuracy.While this approach has the advantages of being simple and inexpensive,it has some less than ideal characteristics. For example, errors in thedelineation of the heater plate 2 can accumulate over the length of thepagewidth printhead (cumulative chip-misalignment). Another disadvantageis that there is no way to incorporate thermal expansion gaps betweenadjacent subunits to ease problems of thermal expansion mismatch betweenthe material used to form the subunits and the substrate to which thearray is bonded. Another problem is that physically butting the chipscould damage the heater plate edges which have circuitry nearby. Thisproblem also applies to image reading arrays which have photosites orother image-detecting components adjacent their edges. A further problemis that if the precision diced edge of the heater plate 2 is notperfectly vertical, chip to chip stand off can result (that is, theupper surfaces of the heater plates 2 which contain the resistiveelements will not be contiguous with one another thus causing unevenspacing of nozzles along the length of the printhead array).

U.S. Pat. Nos. 4,690,391 and 4,712,018 to Stoffel et al, the disclosuresof which are herein incorporated by reference, disclose a method andapparatus for fabricating long full width scanning arrays for reading orwriting images. For this purpose, smaller scanning arrays are assembledin abutting end-to-end relationship, each of these smaller arrays beingprovided with a pair of V-shaped grooves formed by orientation dependentetching (ODE) and located in an upper, component containing facethereof. An aligning tool having predisposed pin-like projectionsinsertable into the grooves on the smaller scanning arrays is used tomate a series of smaller arrays in end-to-end abutting relationship.Discretely located vacuum ports in the aligning tool are used to drawthe smaller arrays into tight face-to-face contact with the tool until asuitable base is affixed to base surfaces of the aligned arrays and thealigning tool withdrawn.

A limitation of the method of Stoffel et al is that the formation ofgrooves on the circuit surface of each smaller scanning array subunitcan render the fabrication of many subunits from a single waferdifficult. In particular, etching the alignment grooves after formationof the circuitry on the subunit can damage the circuitry, whileformation of the grooves prior to the circuitry requires that aphotoresist layer be deposited on the entire surface of the wafer whichrenders the wafer surface non-planar. It is difficult to accurately formcircuitry on a non-planar wafer. Additionally, both of these processesrequire the steps of applying and patterning a photoresist layer whichtakes time and increases costs. Further, since the planar surfaces ofthe (100) silicon wafers used in the method of Stoffel et al are notperfect (100) planes (due to ingot sectioning tolerances of +/-1/2° inthe process which slices these wafers from a larger silicon ingot), thegrooves created by etching are not perfectly shaped and therefore maynot properly mate with the corresponding alignment structure located onthe aligning tool. Although Stoffel et al state that mechanicalmachining can be used to form the grooves, it would be difficult andtime consuming to form these grooves with a dicing saw in the circuitsurface of each subunit since the grooves cannot extend across theentire surface of the subunit due to the circuitry located thereon.

OBJECTS AND SUMMARY OF THE INVENTION

An object of the present invention is to provide a method of fabricatingan extended array from a plurality of discrete subunits whereby eachsubunit is precisely located in the extended array.

Another object of the present invention is to provide a method offabricating an extended scanning array from a plurality of discretereading or writing subunits whereby a thermal expansion gap can beincorporated between each subunit in the array.

Another object of the present invention is to provide a method offabricating an extended scanning array from a plurality of discretereading or writing subunits whereby individual subunits never touch eachother, thus eliminating the possibility of damaging the circuitrycontained on these subunits.

A further object of the present invention is to provide a method offabricating an extended scanning array from a plurality of discretereading or writing subunits whereby individual chip misalignments arenon-cumulative.

To achieve the foregoing and other objects, and to overcome theshortcomings discussed above, the present invention makes use of forminga precision alignment structure on a second surface of each discretesubunit, the subunit including a plurality of components such as, forexample, photosites, heater elements or channels, on a first, oppositesurface thereof, and aligning a plurality of discrete subunits into anextended array by placing the second surface of each discrete subunitonto an alignment substrate and engaging the precision alignmentstructure on each discrete subunit with a corresponding alignmentstructure on the alignment substrate. After an extended array ofsubunits having a desired length is formed, the discrete subunits arebonded, for example, to a base, to form, for example, an integralextended reading or writing array. By arranging the correspondingalignment structure on the alignment substrate so that adjacentalignment structures are spaced a distance apart from one another whichis greater than the width of a discrete subunit, gaps can be providedbetween each discrete subunit in the extended array to allow for thermalexpansion, prevent contact of adjacent subunits and prevent cumulativealignment errors. Additionally, by precisely forming the alignmentstructure extending from a front side to a rear side on the secondsurface of each subunit by using a precision dicing saw and thecorresponding alignment structure on the alignment substrate by, forexample, electroplating or thick film mask deposition techniques, eachdiscrete subunit is precisely located within the extended array.

BRIEF DESCRIPTION OF THE DRAWINGS

A preferred embodiment of the invention will be described in detail withreference to the following drawings in which:

FIG. 1 is a front view illustrating a method of forming an extendedprinthead array by butting adjacent printhead subunits to one another;

FIG. 2 is a front view of a printhead subunit including a notch in itsupper surface which is usable in the present invention;

FIG. 3 is a front view of an assembly step of fabricating an extendedarray of subunits whereby subunits having a single notch in their uppersurface are engaged with corresponding alignment structure on analignment substrate;

FIG. 4 is a front view of an assembly step in a method of fabricating anextended array of subunits whereby two notches are formed on the uppersurface of a subunit which is engaged in slots formed on an alignmentsubstrate; and

FIG. 5 is an isometric view of the alignment substrate used in themethod illustrated in FIG. 4.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 2 shows a front view of a printhead subunit formed by a firstmethod of the present invention. Subunit S' includes an actuator plate 2which includes actuating elements 3 such as, for example, resistiveheating elements having passivated addressing electrodes attachedthereto and a channel plate 4 including a plurality of parallel channels6 which form passageways between an ink nozzle and a supply of ink.Parallel channels 6 are formed on a first or base surface of channelplate 4 and can be supplied with ink by a fill hole (not shown) whichextends through channel plate 4 from its upper, or second surface to thebase surface and fluidwise communicates with channels 6. Ink could alsobe supplied to channels 6 from the sides or rear of channel plate 4.This printhead subunit can be formed by methods described in U.S. Pat.No. 4,851,371 to Fisher et al (the disclosure of which is hereinincorporated by reference). In the present invention, the previouslydescribed methods of fabricating printhead subunits are modified toinclude the step of forming a precision alignment structure, such asnotch 16, on the second, or upper surface of the channel plate 4. Notch16 could have a depth on the order of 30 microns, although the depthdimension is not critical. Notch 16 is preferably formed by a precisiondicing saw although other techniques can be used for forming notch 16such as laser machining techniques or orientation dependent etching. Anadvantage of using a precision dicing saw is that notch 16 can be formedduring the operation of dicing out the printhead from a silicon wafer sothat no additional saw set up is required.

Although the embodiment illustrated in FIGS. 2 and 3 show notch 16 to beformed in the edge of channel plate 4 and extending entirely across theupper surface of each channel plate from a front side to a rear side, itis understood that notch 16 could be formed anywhere in the uppersurface of channel plate 4 as long as it does not interfere with thefill hole (if one exists) in the upper surface of channel plate 4. Whileformation of notch 16 in the edge of each channel plate is advantageousbecause it assures that the precision alignment structure is located inthe same position relative to the components (in this example channels6) for each subunit, when all of the subunits to be formed into an arraywill be fabricated from the same wafer, the formation of the notch onthe edge of each subunit is not necessary. In particular, when aprecision dicing saw is used to form the notches in the subunits duringthe operation of dicing out the printheads from a silicon wafer, thelocation of each notch on each printhead subunit relative to thechannels in that subunit will be the same for every subunit formed fromthe same wafer because of the stepping accuracy of the precision dicingsaw. That is, since the stepping accuracy of commercially availabledicing saws is within +/-1/2 microns, the notch location will be thesame relative to the channels for every subunit formed from the samewafer whether or not the notch is located on the edge of each channelplate. Thus, it is seen how the present invention makes use of highprecision commercially available dicing saws to enable the formation ofprecisely aligned extended arrays of subunits.

As illustrated in FIG. 3, subunit S'₁ is then flipped as before butinstead of physically butting the printhead subunit to a neighboringprinthead subunit, the precision placed notch 16 is butted to acorresponding alignment structure such as detente 20 located on an uppersurface of an alignment substrate 18. Once printhead subunit S'₁ isbutted against detente 20, additional printhead subunits S'₂, S'₃ . . .S'_(N) are butted against corresponding alignment substrates until anextended array of subunits having a desired length is formed. Thisoperation can be performed using a modified commercial chip handlingrobot as described in U.S. Pat. No. 4,975,143 to Drake et al, issued onDec. 4, 1990 and assigned to the same assignee as the present invention.The process disclosed in U.S. Pat. No. 4,975,143 forms a photoresistmaterial layer to form keys or keyways in the photoresist materiallayer. Once the printhead subunit is pushed in place, a vacuum hold downlocks its position until fabrication of the extended array is complete.The vacuum hold-down operates by applying a vacuum through bores 19formed in alignment substrate 18. Bores 19 extend through alignmentsubstrate 18 to the upper surface thereof so that the vacuum will beapplied to each subunit to hold it in place. After an extended array ofthe desired length is formed, adhesive 14 (see FIG. 1) is applied to thebottom of the heater plate 2, at which point a bonding substrate 12 isapplied to complete the mounting process. Adhesive 14 can be, forexample, a heat curable adhesive.

An alternative embodiment, wherein an alignment structure is formed onboth sides of the upper surface of a channel plate, is illustrated inFIGS. 4 and 5. In this second embodiment, first and second notches 16a,16b are formed on opposite sides of the upper surface of the printheadsubunit S"₁, S"₂ . . . S"_(N). The printhead subunit is then flipped andinserted into a slot 26 which is part of a raised pattern formed on theupper surface of alignment substrate 18. In this manner, first andsecond notches 16a, 16b contact first and second sides of the slot 26 sothat the upper surface of the channel plate 4 is completely captured bythe corresponding alignment structure.

The accuracy of alignment of each printhead subunit is limited by theprecision with which the corresponding alignment structure is formed onthe alignment substrate 18. By using precision deposition techniquessuch as electroplating to form detentes 20 or pattern 24 containingslots 26a, 26b, 26c . . . 26n, the positioning of each printhead subunitis highly accurate. Although electroplating is one preferred method offorming the corresponding alignment structure on alignment substrate 18,other processes such as thick film photopatterning techniques can alsobe utilized. By precisely locating each corresponding alignmentstructure on the alignment substrate 18, any discrepancies which existin each printhead subunit S' or S" do not accumulate, as in the buttingmethod, but instead are limited to only the printhead subunit in whichsuch discrepancies exist.

In the above described fabrication processes, the channel plates 4 havea width slightly less than each heater plate 2 and thus the width ofeach printhead subunit is equal to the width W of each heater plate 2.By spacing adjacent corresponding alignment structures 20 or 24 onalignment substrate 18 a distance D which is greater than the width W ofeach printhead subunit, a gap is provided between each printheadsubunit. This gap prevents adjacent heater plate edges from touching oneanother, thus avoiding damage to the circuitry contained on heaterplates 2 and also providing a thermal expansion gap between adjacentprinthead subunits.

By utilizing an alignment substrate having a precisely formed alignmentfeature such as, for example, equally spaced detentes 20, the presentinvention allows precision, non-cumulative, non-contact alignment ofprinthead subunits to form a printhead array. Unlike previously usedprocesses of butting adjacent subunits to one another, the presentinvention eliminates the cumulative errors that result when even asingle subunit in an array has a non-uniform width or a non-verticalbutting surface. With the present invention, each subunit is accuratelylocated in the array of subunits. Additionally, use of the alignmentfeature on the alignment substrate eliminates the possibility of damagewhich can occur when adjacent subunits are butted to one another whileallowing for the provision of expansion gaps in the printhead array.

While the present invention is described with reference to thermal inkjet printheads, this particular embodiment is intended to beillustrative, not limiting. For example, the present invention alsofinds use in the fabrication of ink jet printheads wherein the actuatingelements on plate 2 are piezoelectric transducers. Additionally, thepresent invention can be utilized to form notches using a precisiondicing saw in heater plates or image sensor subunits which are thenaligned in an extended array. In particular, either a plurality ofheating elements (as disclosed in the above-cited U.S. Pat. Nos.4,601,777 to Hawkins et al and 4,851,371 to Fisher et al) or imagesensing components such as, for example photosites (as disclosed in theabove-cited U.S. Pat. Nos. 4,690,391 and 4,712,018 to Stoffel et al)would be formed on a first surface of each subunit and one or morenotches would be diced out of a second, oppositely facing surface ofeach subunit. In this example, the second surfaces of the subunits whichcontain the notch or notches could be bonded directly to the alignmentsubstrate because the opposite (or first) surface of each subunitcontains the active components (heating elements or photosites). If thesubunit containing the precision diced notch is a heater plate, theheater plate could be aligned on and bonded to the alignment substrateeither before or after having a channel plate bonded thereto. Channelplates having precision diced notches could also be aligned on thealignment substrate without having a heater plate bonded thereto,although the channel plates would not usually be bonded to the alignmentsubstrate because they include an ink fill-hole on the second surfacethereof. However, channel plates could be bonded to the alignmentsubstrate if ink was supplied to each channel plate from the sides orfrom behind or if a fill-hole is also provided through the alignmentsubstrate. See, for example, U.S. Pat. No. 4,612,554 to Poleshuk. Thepresent invention can also be used to form pagewidth printheads whereindiscrete printhead subunits are provided in a staggered arrangement onopposite sides of a common bonding substrate. Various modifications maybe made without departing from the spirit and scope of the invention asdefined in the appended claims.

What is claimed is:
 1. A method of fabricating an extended array from aplurality of discrete subunits, said discrete subunits having first andsecond oppositely facing surfaces with a plurality of components on saidfirst surface, said method comprising the steps of:a) forming aprecision alignment structure on at least one side of the second surfaceof each discrete subunit by dicing at least one notch in said at leastone side of said second surface with a dicing saw; b) placing the secondsurface of a discrete subunit on an elongated alignment substrate, saidalignment substrate having a plurality of corresponding alignmentstructures; c) engaging said at least one notch on the second surface ofsaid discrete subunit with one of said corresponding alignmentstructures on said alignment substrate; d) repeating steps (b) through(c), by placing subsequent discrete subunits on said alignment substrateuntil an extended array of subunits having a desired length is formed;and (e) bonding the discrete subunits to a support to form an integralextended array.
 2. The method according to claim 1, wherein saidcorresponding alignment structure on said alignment substrate includes aseries of equally spaced detentes, said engaging step including buttingsaid notch against a corresponding detente.
 3. The method according toclaim 1, wherein a first notch is formed on said one side of the secondsurface of each discrete subunit and a second notch is formed on anotherside of the second surface of each discrete subunit.
 4. The methodaccording to claim 3, wherein said corresponding alignment structure onsaid alignment substrate includes a raised pattern having a series ofequally spaced slots, said engaging step including inserting the uppersurface of each discrete subunit into a corresponding slot so that saidfirst and second notches are captured between first and second sides ofsaid corresponding slot.
 5. The method according to claim 1, whereinsaid discrete subunit has a width which is less than a distance betweenadjacent corresponding alignment structures on said alignment substrateso that the integral extended array includes expansion gaps betweenadjacent subunits.
 6. The method according to claim 1, furthercomprising applying a vacuum through at least one vacuum hole associatedwith each corresponding alignment structure on the alignment substrateso that each discrete subunit is secured to said alignment substrateafter engagement therewith.
 7. The method according to claim 1, whereinsaid support is said alignment substrate, and one of said secondsurfaces of said plurality of discrete subunits and said alignmentsubstrate has a curable adhesive applied thereon, said bonding stepincluding curing said adhesive so that each discrete subunit is bondedto said alignment substrate.
 8. The method according to claim 1, whereinsaid discrete subunits are image sensor subunits and said plurality ofcomponents is a linear array of photosites including supportingcircuitry.
 9. The method according to claim 1, wherein said discretesubunits are heater plate subunits and said plurality of components isan array of heating elements having passivated addressing electrodes.10. The method according to claim 1, wherein said discrete subunits arechannel plate subunits and said plurality of components is an array ofchannel forming grooves.
 11. The method according to claim 1, whereinsaid at least one notch extends entirely across said second surface ofeach discrete subunit from a front side to a rear side of said secondsurface.
 12. A method of fabricating an extended printhead array from aplurality of discrete printhead subunits, said printhead subunitscomprising an actuator plate subunit including a plurality of actuatingelements on an upper surface thereof and a channel plate subunit havinga plurality of channels corresponding in number and position to saidactuating elements on a base surface thereof, the upper surface of saidactuator plate subunit being attached to the base surface of saidchannel plate subunit to define a printhead subunit having saidplurality of channels with one of said actuating elements incommunication with each channel, said method comprising the steps of:a)forming a precision alignment structure on at least one side of an uppersurface of each channel plate subunit; b) placing the second surface ofthe channel plate subunit of a discrete printhead subunit on anelongated alignment substrate, said alignment substrate having aplurality of corresponding alignment structures; c) engaging theprecision alignment structure on the upper surface of said channel platesubunit of said discrete printhead subunit with one of saidcorresponding alignment structures on said alignment substrate; d)repeating steps (b) through (c), by placing subsequent discrete subunitson said alignment substrate until an extended array of subunits having adesired length is formed; and (e) bonding the discrete subunits to asupport to form an integral extended array.
 13. The method according toclaim 12, wherein said precision alignment structure is formed on bothsides of the upper surface of each channel plate subunit.
 14. The methodaccording to claim 12, wherein said precision alignment structure isformed by dicing at least one notch on said at least one side of theupper surface of each channel plate subunit with a dicing saw.
 15. Themethod according to claim 14, wherein a single notch is formed on oneside of the upper surface of each channel plate subunit.
 16. The methodaccording to claim 15, wherein said corresponding alignment structure onsaid alignment substrate includes a series of equally spaced detentes,said engaging step including butting said notch against a correspondingdetente.
 17. The method according to claim 14, wherein a first notch isformed on said one side of said upper surface of each channel platesubunit and a second notch is formed on another side of said uppersurface of each channel plate subunit.
 18. The method according to claim17, wherein said corresponding alignment structure on said alignmentsubstrate includes a raised pattern having a series of equally spacedslots, said engaging step including inserting the upper surface of thechannel plate subunit of each discrete printhead subunit into acorresponding slot so that said first and second notches are capturedbetween first and second sides of said corresponding slot.
 19. Themethod according to claim 12, wherein said actuator plates have a widthwhich is less than a distance between adjacent corresponding alignmentstructures on said alignment substrate so that the integral extendedprinthead array includes expansion gaps between adjacent printheadsubunits.
 20. The method according to claim 12, further comprisingapplying a vacuum through at least one vacuum hole associated with eachcorresponding alignment structure on the alignment substrate so thateach discrete printhead subunit is secured to the alignment substrateafter engagement therewith.
 21. The method according to claim 12,wherein said support is a host substrate, and said step of bondingcomprises applying a curable adhesive to a base surface of said actuatorplate subunits, contacting said host substrate with the base surface ofsaid actuator plate subunits and curing said adhesive.
 22. The methodaccording to claim 12, wherein said actuator plate subunits are heaterplate subunits and said actuating elements are heating elements havingpassivated addressing electrodes attached thereto.
 23. The methodaccording to claim 12, wherein said integral extended printhead arrayhas a length corresponding to a width of a page.
 24. The methodaccording to claim 14, wherein said precision alignment structuresextends entirely across said upper surface of each channel plate subunitfrom a front side to a rear side of said upper surface.
 25. A method offabricating a pagewidth thermal ink jet printhead from a plurality ofdiscrete thermal ink jet printhead subunits, each thermal ink jetprinthead subunit comprising a heater plate subunit having a pluralityof resistive elements on an upper surface thereof and a channel platesubunit having a plurality of channels corresponding in number andposition to said resistive elements on a base surface thereof, the uppersurface of said heater plate subunit being attached to the base surfaceof said channel plate subunit to define a thermal ink jet printheadsubunit having said plurality of channels with one of said resistiveelements in communication with each channel, said method comprising thesteps of:a) forming a precision alignment structure on an upper surfaceof each channel plate subunit, said precision alignment structure beingat least one notch formed by a precision dicing saw; b) placing theupper surface of a discrete thermal ink jet printhead subunit on anelongated alignment substrate, said alignment substrate having aplurality of corresponding alignment structures; c) engaging said atleast one notch on the upper surface of said discrete thermal ink jetprinthead subunit with one of said corresponding alignment structures onsaid alignment substrate; d) repeating steps (b) through (c), by placingsubsequent discrete thermal ink jet printhead subunits on said alignmentsubstrate until a pagewidth printhead is formed; and e) bonding thediscrete thermal ink jet printhead subunits to a base substrate to forman integral pagewidth printhead.
 26. The method according to claim 25,wherein said at least one notch extends entirely across said uppersurface of each channel plate subunit from a front side to a rear sideof said upper surface.
 27. The method according to claim 25, whereinsaid notch is formed on at least one side of the upper surface of eachchannel plate subunit.
 28. The method according to claim 25, wherein afirst notch is formed on one side of the upper surface of each channelplate subunit, and a second notch is formed on another side of the uppersurface of each channel plate subunit.